Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
Browse
14 results
Search Results
Item Numerical modelling of nanoparticle diffusion and microstructure formation during selective laser melting process(Montana State University - Bozeman, College of Engineering, 2022) Alam, Taosif; Chairperson, Graduate Committee: M. Ruhul AminSelective laser melting (SLM) is a popular metal additive manufacturing technique that has a wide range of industrial applications lately. This additive process allows the development of new metal matrix nanocomposites by fusing metallic powders with nanoparticles. However, the molten pool flow generated by a moving laser heat source has complex fluid dynamics which redistribute the nanoparticles. Consequently, the microstructures of the solidified molten pool are affected by the local distribution of nanoparticles, which is reflected in their mechanical properties. Smaller grains can increase the strength and isotropic behavior of the solid layers. Therefore, the current research aims to numerically investigate the relationships among the SLM process parameters, nanoparticle transport, and microstructure evolution to explore the formation of nanocomposites. The current study formulated a three-dimensional computational fluid dynamics (CFD) model of the SLM process in a commercial software package, ANSYS FLUENT. A volumetric laser heat source model melted the aluminum alloy powders and the underlying solid substrate. The difference between the powder and the solid or liquid state of the metal alloy was defined using an effective thermal conductivity model. Lagrangian particle transport calculation was performed to track TiB 2 nanoparticles in the molten pool. This model was coupled with a 2D Cellular Automata (CA) model to simulate the solidified microstructure using MATLAB. Finally, a detailed parametric analysis was conducted to study the effects of varying laser power, scanning speed, and preheating temperature. The numerical results showed that the maximum temperature and Marangoni convection in the molten pool increased at higher laser powers, higher preheating temperatures, and lower scanning speeds. The particle-voided region was significantly large with high Marangoni convection but decreased with weaker Marangoni convection. The simulated microstructure was dominated by large columnar grains when nanoparticles were not considered. The introduction of nanoparticles disrupted the columnar grain growth by promoting small, randomly oriented, equiaxed grains. A decrease of 30%-40% in average grain diameter was measured at the cross-section of the solidified layer when nanoparticles were present. The qualitative comparison of the microstructures showed that the grains were smaller in the uniformly distributed particle region compared to the particle-voided region.Item Intrusive uncertainty quantification method for simulations of gas-liquid multiphase flows(Montana State University - Bozeman, College of Engineering, 2020) Turnquist, Brian Robert; Chairperson, Graduate Committee: Mark Owkes; Mark Owkes was a co-author of the article, 'MULTIUQ: an intrusive uncertainty quantification tool for gas-liquid multiphase flows' in the journal 'Journal of computational physics' which is contained within this dissertation.; Mark Owkes was a co-author of the article, 'A fast, density decoupled pressure solver for an intrusive stochastic multiphase flow solver' submitted to the journal 'Journal of computational physics' which is contained within this dissertation.; Mark Owkes was a co-author of the article, 'MULTIUQ: a software package for uncertainty quantification of multiphase flows' submitted to the journal 'Computer physics communications' which is contained within this dissertation.; Mark Owkes was a co-author of the article, 'Exploration of basis functions for projecting a stochastic level set in a multiphase flow solver' submitted to the journal 'Atomization and sprays' which is contained within this dissertation.Simulations of fluid dynamics play an increasingly important role in the development of new technology. For example, engineers may need to simulate an atomizing jet to create a better direct injection system for improving fuel economy in a vehicle, or to more efficiently spray water for building fire mitigation systems. The increased use of computational fluid dynamics requires improvements in methodology to improve simulation efficiency and accuracy. We can extract a great deal from these models, including uncertainty information. Although simulation of gas-liquid multiphase flow scenarios are common, most are deterministic in nature. Model parameters, like fluid density or viscosity, are assumed to be known and fixed. But this is not usually the case, and a research gap exists for uncertainty analysis in these simulations. For efficient performance, an intrusive approach is used to create a multiphase solver capable of uncertainty analysis. Variables of interest, such as velocity and pressure, are converted into stochastic variables which are allowed to vary in an added uncertainty dimension. Variability is then added to fluid parameters or initial/boundary conditions and a simulation is run which produces stochastic results. To verify the solver, several cases are presented which compare the ability of the solver against analytic solutions. Once satisfied with the ability of the solver, we can answer questions about more complex scenarios. For instance, we may question how uncertainty about the surface tension force may affect the atomization of a jet and find that fluids with a lower surface tension coefficient breakup sooner (as expected). We could also consider scenarios that may not have such an obvious outcome, such as imposing uncertainty about the density ratio for an atomizing jet to determine the effect of running simulations at low vs high density ratios. multiUQ is capable of producing accurate results of real world situations. As a tool it can provide additional insight into understanding complicated multiphase flow systems.Item Comparative analysis of a design tool to field study data for an unglazed transpired solar collector(Montana State University - Bozeman, College of Engineering, 2016) Guenette, Chelsea Lynn; Chairperson, Graduate Committee: Kevin AmendeEnergy consumption and emission concerns have come to the forefront of political and public attention. The adoption of building energy standards such as ASHRAE Standard 90.1 have helped guide the building industry by setting increasingly stringent building energy performance requirements. In order to meet these ever increasing energy standards, research and development of energy efficient technologies have become a priority. One of these is the unglazed transpired solar collector (UTSC) which is particularly useful in sunny, cold climates such as Bozeman, Montana. This research intends to bridge the gap between theoretical models and field studies by comparing an accepted UTSC model within a commercially available energy modeling software -- EnergyPlus -- to experimental data collected at Jabs Hall in Bozeman, Montana. An energy model was created to represent a UTSC and its associated building in a commercially available software. Weather and operating data for the UTSC was collected on site. The collected weather data was used to create a custom input weather file for the energy model. The collected operational data was used to characterize the UTSC performance and compare to the energy model results. Limitations for both the energy and data acquisition make it difficult for the results to be compared directly. However, conclusions were drawn about UTSC integration into building systems.Item Investigation of the effect of in-plane fiber waviness in composite materials through multiple scales of testing and finite element modeling(Montana State University - Bozeman, College of Engineering, 2015) Lerman, Michael William; Chairperson, Graduate Committee: Douglas S. CairnsDefects in materials can reduce strengths and lifetimes of manufactured parts. The number of possible defects increase with the complexity inherent in composite materials. The wind industry uses composite wind turbine blades in which the manufacturing process induces a number of defects. In order for the wind industry to continue sustainable expansion, the effects of defects must be better understood. In-plane (IP) fiber waviness is the focus of this work. The three main parts of this work include testing on the coupon level, modeling on the coupon level, and testing of beams in four-point bending (with and without defects). The coupon level testing includes partial IP waves, similar to those in manufactured parts, rather than full width IP waves. This allows investigation into complex interactions and varying failure mechanisms caused by the fiber misalignment gradient. Partial waves are also modeled to both validate testing as well as to increase robustness of a previously developed progressive damage modeling method. Lastly, a sandwich beam test specimen for testing in 4-point bending is developed to investigate the effects of fiber waviness in both tension and compression when loaded in flexure.Item Three dimensional finite element analysis of matrix cracks in multidirectional composite laminates(Montana State University - Bozeman, College of Engineering, 1993) Shrinivas, ModayurItem Numerical study of conjugate heat transfer in a continuously moving metal during solidification(Montana State University - Bozeman, College of Engineering, 1998) Greif, DavidItem One-dimensional model for laser generated elastic waves in a solid layer : the illuminated surface of which is constrained by a transparent liquid medium(Montana State University - Bozeman, College of Engineering, 1989) Cherukuri, Harischandra PrasadItem A new iterative method for solving simultaneous linear equations with direct applications to three-dimensional heat conduction problems(Montana State University - Bozeman, College of Engineering, 1980) Horning, Rodney PaulItem A mathematical model of laser ablation applied to ultrasonics in liquid mercury(Montana State University - Bozeman, College of Engineering, 1996) Garwick, Stephen EugeneItem Frequency response analysis of the in-vivo human skull(Montana State University - Bozeman, College of Engineering, 1977) Grammens, Gerald Martin